Page printer

ABSTRACT

A high speed non-impact printing device, that generates characters of high quality on a photosensitive medium in a predetermined page format. A high intensity projection kinescope is utilized as a light source and an aperture and lens array provides substantially parallel light through a moveable character matrix. Transparent Characters on an opaque background are arranged in rows and columns on a matrix, all characters of one row being of the same kind, the number of rows being equal to the number of different characters in the set and the number of columns being equal to the maximum number of characters per line on the printed page. The matrix is moved one step at a time and all character positions that agree with the desired text are illuminated. A mini computer with sufficient memory capacity to store a page of characters is utilized to control the printing operation.

United States Patent 1 Nielsen [4 1 Feb. 12,1974

[ PAGE PRINTER Asger Torben Nielsen, 3836 Front St., San Diego, Calif. 92103 [22] Filed: Apr. 13, 1972 [21] Appl. No.: 243,561

[76] Inventor:

521 US. Cl. 95/45 51 Int. Cl B41b 19/06 [58] Field of Search 95/45; 340/324, 378

[56] References Cited UNITED STATES PATENTS 3,330,190 7/1967 Taillie 95/4.5 3,504,609 4/1970 Donald 95/45 Primary Examinerlohn M1 Horan [57] ABSTRACT A high speed non-impact printing device, that generates characters of high quality on a photosensitive medium in a predetermined page format. A high intensity projection kinescope is utilized as a light source and an aperture and lens array provides substantially parallel light through a moveable character matrix. Transparent Characters on an opaque background are arranged in rows and columns on a matrix, all characters of one row being of the same kind, the number of rows being equal to the number of different characters in the set and the number of columns being equal to the maximum number of characters per line on the printed page. The matrix is moved one step'at a time and all character positions that agree with the desired text are illuminated. A mini computer with sufficient memory capacity to store a page of characters is utilized to control the printing operation.

7 Claims, 7 Drawing Figures P'ATENTEBFEB 1 2:914

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PAGE PRINTER BACKGROUND OF THE INVENTION This invention relates to computer controlled high speed printing devices and more specifically to the type that projects Characters from a transparency to a light sensitive medium. Equipments that solve the general problem of printing alphanumeric information under computer control have been known for several years and many different techniques are being used with various degrees of success.

Some of. the earliest devices utilized a chain of metal characters that moves continuously in :a direction perpendicular to a paper strip. Electrically energized hammers bring type and paper in contact, thus causing an imprint to be made on the paper. When caracters that represent the entire alphabet have passed by the paper, one line of printed text has been completed and the paper is advanced oneprint line ready for the next operation. Characters printed this way has a tendency to appear smeared, because the type is moving while the hammer forces it against the paper. The device is rather slow (6-7 seconds per page) in'relation to the operating speed of the computer.

Later electronic devices known as microfilm recorders'came into use. Alphanumeric characters are generated by various means on the face of a cathode ray tube and photographed on microfilm. The devices known as COM equipmentare extremely fast, four to 10 pages per second, but are very expensive and require frequent maintenance. Many of them also suffer from relatively poor character quality, and because the amount of light that can be generated on a CRT is very limited, only extremely sensitive film can be used at these high speeds of operation. As film sensitivity is increased it is a general rule for silver halide film that resolving power is reduced while cost is increased.

Light emitting diodes are used in some equipments instead of the CRT. They emit light in the red or orange end of the spectrum and must therefore also use silver film. Character quality is poor, because each character is composed of a finite number of elements usually 5 X 7 or at the most 7 X 11'.

Lasers are also applied to this field as the light source. Its intensity is higher by several orders of magnitude; but deflecting a light bear'n at a high rate of speed is much more difficult than deflecting an electron beam. Either mechanical means or acoustical deflection cells have to be used making stability a major problem.

Also, since alphanumeric characters are generated from individual dots where each dot corresponds to the laser beam being focused on the photosensitive medium, increase in cost and in the time spent on each character sets a limit for how many elements can be used for each character.

It is generally recognized that to obtain an acceptable character quality it is necessary to utilize at least 25 X 25 elements and preferably as high as '100 X 100 elements for each character.

SUMMARY OF THE INVENTION The present invention is an electro-optical recording device, here alphanumeric characters and other symbols are transferred from a matrix, located adjacent to the phosphor of a high intensity cathode ray tube, to a light sensitive medium such as a photographic film or an electrostatic or photocromic recording surface.

The character matrix is held stationary, while light is generated in rectangular patterns on the phosphor behind each character in succession, until all characters, that have a code and location combination that agrees with the information stored in the electronic memory device, have been displayed. The character matrix is then advanced one step and light patterns are again generated at new locations according to' the stored information. This mode of operation continues until all rows of characters on the matrix have been located opposite allcharacter positions on the page format. Next, the photographic medium is moved and an unexposed area of the medium is moved into position for the recording of a new page and at the same time the electronic memory has been updated with new information.

It is therefore an object of this invention to provide a high speed non-impact page printing device that can generate characters of much improved quality.

It is a further object of the invention to provide a method of generating characters utilizing a considerably higher intensity light source than has been possible before, in order to expose photographic film with lower sensitivity than silver halide film.

It is still a further object of the invention to provide an electronic printing device, where character position depends much less on the stability of the cathode ray tube deflection circuits than heretofore possible.

It is also an object of the invention to provide a character generator system utilizing a cathode ray tube, where character resolution is independent of the size of the light spot'create d on the phosphor and also independent of the grain size of the phosphor.

It is also an object of the invention to provide a microfilm printer system of relatively low cost; in production because'it contains fewer parts of lower cost than other microfilm printers and in use because it can utilize photographic film having lower sensitivity and requiring simpler development methods.

It is also an object of the invention to provide a microfilm printer where the character set can be easily and economically expanded or replaced.

It is an additional object of the invention to provide a circuit, that enables a fast settling time of the cathode ray tube deflection circuits.

It is also an object of the invention to provide a simplified method for verifying proper alignment between the display patterns on the face of the cathode ray tube and the character matrix.

This invention, however, both as to its originality and to its method of operation and additional objects and embodiments, will best be understood from the following description, when read together with the associated drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a blockdiagram of the preferred embodi-v ment of the invention.

FIG. 2 is a drawing of a section of the aperture and lens array.

FIG. 3 represents a partial view of the character matrix.

FIG. 4 is a block diagram of the transient detector.

FIG. 5 is an illustration of the curve forms generated by the transient detector.

FIG. 6 is an illustration of the major components, that are used for the deflection circuit alignment.

FIG. 7 shows the optical components used in sensing the accuracy of the CRT alignment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Digital information representing alphanumeric characters to be printed is stored on magnetic tape. A reel of tape is placed on the magnetic tape deck 4, shown in FIG. 1, and is read into the computer 2, where it is rearranged and organized to suit the printing sequence. It is stored in the electronic memory circuits of the computer in such a way, that the address in storage is related to the character position on the page and the contents at each address is related to the code of the character to be printed.

The X position register 6 on FIG. 1 is eight bits long and the Y position register 8 is six bits long. The eight bits in register 6 are used for control of eight electronic switches in D-A converter 10, while the six bits in register 8 are used for control of the six electronic switches in D-A cpnverter 12.

The output of 10, which is a voltage proportional to the digital contents stored in 6, is fed into current amplifier 14, which in turn controls the current through the horizontal windings of deflection yoke 30. In a similar way the output voltage from 12 controls the output of current amplifier l6 and thereby the vertical deflection current through yoke 30.

Horizontal scan generator 18 generates a triangular wave at a frequency of some few MHz and vertical scan generator 20 generates a sawtooth waveform that has a duration of some few microseconds.

Unblank control circuit 26 is energized at the same time as circuits 18 and 20 and generates a positive going pulse, that has the same time duration as the slow rising ramp of the sawtooth from vertical scan generator 20. Its amplitude is in the order of 50 75 volt. The output of 18 is amplified in current amplifier 22 and the output of 20 is amplified in current amplifier 24. The two scan signal currents control the horizontal and vertical deflection fields in deflection yoke 32. Cathode ray tube 28 is a projection kinescope producing considerably higher light output than high resolution display cathode ray tubes of the types used in microfilm recorders.

The AZ? and 7 WP 4 manufactured by RCA are representative types. The dot size on kinescopes is considerably larger than on high resolution tubes. However, because characters are not displayed directly on the phosphor, but instead projected onto the photo sensitive media utilizing the exited phosphor as a light source, character resolution and quality is not a function of the stroke width. For this reason a simpler and therefore less expensive electron gun such as the type that is used in projection kinescopes can be used for this application. For the same reason it is not necessary to provide circuits for the control of electron optical focus as a function of the deflection amplitude from the center of the tube, thus further assisting in cost reduction.

When computer 2 issues a command signal on wire 3, horizontal scan 18, vertical scan and unblank control circuit 26 begin to function simultaneously. The result is that a small rectangle of light is generated on the tube face 34 at a location that is determined by the position information that has been stored in registers 6 and 8.

An aperture and lens array 36 is mounted a short distance in front of face plate 34. It is shown in more detail 5 on FIG. 2, where 36 is the base material i.e., molded plastic. On the flat side of the array which is facing the cathode ray tube, an opaque layer 62 has been deposited. A number of rectangular openings 64 in the opaque coating are located opposite the curved lens surfaces in such a way, that the center line of each pair (lens and aperture) is directed toward the center of projection lens 40 on FIG. 1. The aperture serves to eliminate light rays that would emerge from the corresponding lens in a direction that would not be parallel to the center line 68. It thereby prevents stray light from one area on the face plate 34 from reaching projection lens 40 through one of the adjacent lenses in the array. The character matrix 38, where alphanumeric characters and other graphic symbols appear. as transparent areas on an opaque background, is located in front of the aperture and lens array 36. The character matrix 38, which is shown in part on FIG. 3, is ideally a photographic negative made on a thin, flexible material such as Mylar (trade name of Du Pont). It can be seen from FIG. 3, that rows of characters of the same kind 74 and 76 are located on the film strip between two rows of perforations 72. The number of characters in each row corresponds to the maximum number of character per print line on the finished page.

On FIG. 1 the character matrix film strip is supported by two sprocket rollers 45, that are driven by motors 46 and 50. The movementof each motor is controlled by control circuits 44 and 48. The two motors 46 and 50 are connected directly to the sprocket rollers 45 and are ideally stepping motors. A small holding current through the proper windings of the motor prevents the character matrix from drifting away from the desired position between steps.

The two sprocket rollers are mounted on the drive shafts in such a way, that the holding torque produced by the stepping motors causes a slight tensile force in the film strip, thus keeping it flat. If the holding current through motor 46 is larger than the holding current through motor 50, the registration of the film strip will be controlled by motor 46 and its associated sprocket roller. The light passing through projection lens 40 is focused on the photo sensitive medium 42,which for ex. can be a 16 mm film strip. It is driven by motor 54 which in turn is controlled by page advance control circuit 52.

In operation the alphanumeric characters, that constitute one page (up to 64 lines and up to 132 characters), are stored in code form in the electronic memory of the mini computer. The sequence, in which they are stored, corresponds to the sequence, in which characters are read on a printed page.

Initially the character matrix has the row of As, 74

on FIG. 3 located opposite the top row of lenses on the lens and aperture array, 36 on FIG. 1.

A binary counter (not shown) with a maximum count, that corresponds to the number of rows on the character matrix, is initially at a count of all ZERO's.

65 Position registers 6 and 8 are also set to all ZEROs..

When printing begins the character code in the first cell of the memory is compared to the contents in the binary counter. If the two agree a scan cycle is initiated.

If not, position register 6 is advanced one step and a comparison is made with the contents of the second cell. This way the first 132 positions in the memory are checked against the binary counter. Next the position register 6 is reset to ZERO, position register 8 is advanced one step and the binary counter is advanced by one count.

The character code in memory cell 133 is compared to the binary counter and a scan cycle is initiated,if there is agreement. Otherwise register 6 is advanced and the comparison is made with the contents of memory cell 134.

This way all memory cells are interrogated and scan cycles are inititated, wherever there is agreement between the character code in the memory cell and the contents of the binary counter. At the end of this operation position registers 6 and 8 are reset to ZERO, the binary counter is set to a ONE and the character matrix is advanced one step in the direction of arrow 78, on FIG. 3. Comparison between character codes in memory cells and the binary counter takes place again and scan cycles are initiated wherever there is agreement.

After the character matrix has been advanced a number of steps, that corresponds to one less than the number of rows of characters on the matrix, a page has been completed and film strip 42 on FIG. 1 is advanced one frame.

On FIG. 4 is shown a blockdiagram of the transient detector. The purpose of this device is to sense the point in time, when the magnetic fields created by yoke 30 on FIG. 1 have settled to within a sufficiently small error, after deflection has taken place. The signal, that is generated by the transient detector, is used for control of start of the scan cycle.

On FIG. 4 a dual analog comparator 82, such as Motorola MC 1711, is connected to the output of D-A converter 10 and to the output of summing amplifier 14. A dual comparator is used in order to make the system bipolar. As long as the difference between the two outputs exceeds a few millivolts, the comparator will have a ZERO output, while its output will become a ONE, when the difference is less than a few millivolts. This is shown in more detail on FIG. 5, where 94is the input to the comparator, while 96 is the digital output.

When the deflection system is at rest, input 94 is at ground level below the threshold level 92. When D-A converter 10s output is changed, the input to comparator 82 takes on the value shown as 93 on FIG. 5. This way the threshold level is exceeded because the deflection yoke 30 causes the voltage at the top of resistor to lag the voltage output from 10. As the current through deflection yoke settles,the voltage at the top of resistor 15 approaches the voltage output from 10. This is shown as 95 on FIG. 5. When the threshold level 92 again is crossed, output 96 changes back to a ONE, indicating that the position of the electron beam in the cathode ray tube has reached the desired magnitude to within a precalculated small error.

A signal from the mini computer on line 83 indicates when the transient goes in the opposite direction. An inverter 84 makes the selection of the strobe inputs to the comparator mutually exclusive. The transient detector just described senses the time when the X deflection circuits have settled. A similar circuit is connected to DA converter 12 and to the top of resistor 17. It senses when the settling of the Y deflection circuits is completed. The output from comparators 82 and 86 are taken to a three input NAND gate 88 together with a signal from the mini computer arriving on line 91. This signal is a demand for a character to be generated. It becomes a ONE at the time either the X register or the Y register (6 and 8 on FIG. 1) or both are updated, and it is reset to ZERO after some few hundred nanoseconds.

The result of combining the three signals at the input to gate 88 is that its output remains a ZERO until the last of the three signals has gone to ZERO. At that time 88s output becomes a ONE, which is used for the start of the scan cycle instead of the signal from the mini computer on line 3, FIG. 1.

It should be realized, that the addition of the transient detector to the page printer, is not mandatory for its operation according to the principle of the present invention, but is rather a refinement, that will assist in optimizing the speed of operation of the printer.

On FIG. 6 is shown a front view of the face plate 34 of the cathode ray tube 28. Rectangle 102 indicates the area, that is used in character generation. Outside this area on the horizontal and vertical center axes a line is drawn at four locations 104.

Four sensing devices as shown on FIG. 7, each consisting of a lens 106 and a light sensitive device 108, are directed at and focused on each of the four locations 104. Only when the light, that is generated on the face plate 34, is located precisely at the focal point of lens 106 will photosensor 108 generate an output voltage.

Each of the four photo sensors is connected to a light emitting diode 110 located on the operators control panel at a location remote from the cathode ray tube. Four potentiometer controls, (not shown) two for gain control and two for centering control of horizontal and vertical deflection, are accessible to the operator. They can be used to move the four lines 104 until all four photosensitive devices 108 receive the same amount of light as indicated by the four indicator lights 1 10 having the same brightness.

While there has been described and illustrated specific embodyments of the invention, it will be obvious, that various changes and modifications may be made therein without departing from the field of the invention, which should be limited only by the scope of these claims.

I claim:

1. A non-impact printer utilizing:

a cathode ray tube;

a first deflection system including first deflecting means for independently deflecting the electron beam of said cathode ray tube through angular displacements in two mutually perpendicular directions;

dual position register means coupled to said first deflecting means of said first deflection system according to information received from an external data source;

a second deflection system including second deflecting means for independently deflecting the electron beam of said cathode ray tube describe angular displacement in two mutually perpendicular directions;

scan generator means for controlling said second de flection system causing the electron beam of said cathode ray tube to describe a substantially rectangular pattern;

intensity control circuits means for unblanking said cathode ray tube during the time said rectangular deflection pattern is generated;

a character matrix having transparent characters on an opaque background arranged in rows and columns, all characters of one row being of the same kind, the number of rows being equal to the number of different characters in the set and the number of columns equal to the maximum number of characters per line on the printed page, said character matrix being moveable in a plane parallel 'to the face plate of said cathode ray tube;

multiple collimator lens and aperture means for providing substantially parallel light through the transparent areas of said character matrix, said multiple lens and aperture means being located accurately between said cathode ray tube face plate and said moveable character matrix;

lens means for projecting images of said transparent characters illuminated by light from said rectangular patterns generated 'on said cathode ray tube onto a light sensitive medium;

means for advancing said character matrix in incremental steps of the same amplitude as the distance between said rows of characters and in a direction parallel to said columns of characters;

signal responsive means having means for receiving data from an external source, and operable for controlling said position register means and said character matrix advance means for causing a succession of printed pages to be exposed onto said light sensitive medium.

2. The non-impact page printer of claim 1 wherein:

said first deflection system and first deflecting means consist of a first deflection yoke having first deflection coils and further including a dual digital to analog converter means coupled to dual current amplifier means for controlling the currents through said first deflection coils.

3. The invention set forth in claim 2 additionally including a transient detector comprising:

two dual differential comparator means connected to said first and second digital to analog converter and to said first and second current amplifiers;

inverter means for selecting the output of said comparators according to the magnitude of said data received from said signal responsive means;

AND gate means for assembling the output from said differential comparators with a control signal from said signal responsive means;

means for controlling the timing of said scan and intensity control circuits by the output from said AND gate.

4. The invention set forth in claim 1 additionally including a device for correcting the alignment of the display patterns on said cathode ray tube comprising:

a. means for manually adjusting centering and deflection gain in two mutually perpendicular directions on said cathode ray tube;

b. optical means for sensing the location of light patterns on said cathode ray tube;

0. means for indicating that light is sensed by said optical means. 5. The invention set forth in claim 4 wherein said means for advancing said character matrixcomprises a stepper motor, and

said stepper motor requires at least three pulses to advance said character matrix the equivalent of the distance between said rows of characters, and where said signal responsive means is equipped to select one; two or three of said pulses for advancing said character matrix, and where said signal responsive means controls said digital to analog converter tolocate said rectangular light patterns on said cathode ray tube according to whether one, two or three pulses were selected. 6. The invention set forth in claim 4 wherein said first deflection yoke and said second deflection yoke are replaced by a single deflection yoke, including coils for deflecting said electron beam in two mutually perpendiculardirections and wherein said dual current amplifier is a summing amplifier receiving inputs from said digital to analog converters and from said scan current generators.

7. The non-impact page printer of claim 1 wherein: said second deflection system and second deflecting means consist of second deflection yoke and sec- I 0nd deflection coils. 

1. A non-impact printer utilizing: a cathode ray tube; a first deflection system including first deflecting means for independently deflecting the electron beam of said cathode ray tube through angular displacements in two mutually perpendicular directions; dual position register means coupled to said first deflecting means of said first deflection system according to information received from an external data source; a second deflection system including second deflecting means for independently deflecting the electron beam of said cathode ray tube describe angular displacement in two mutually perpendicular directions; scan generator means for controlling said second deflection system causing the electron beam of said cathode ray tube to describe a substantially rectangular pattern; intensity control circuits means for unblanking said cathode ray tube during the time said rectangular deflection pattern is generated; a character matrix having transparent characters on an opaque background arranged in rows and columns, all characters of one row being of the same kind, the number of rows being equal to the number of different characters in the set and the number of columns equal to the maximum number of characters per line on the printed page, said character matrix being moveable in a plane parallel to the face plate of said cathode ray tube; multiple collimator lens and aperture means for providing substantially parallel light through the transparent areas of said character matrix, said multiple lens and aperture means being located accurately between said cathode ray tube face plate and said moveable character matrix; lens means for projecting images of said transparent characters illuminated by light from said rectangular patterns generated on said cathode ray tube onto a light sensitive medium; means for advancing said character matrix in incremental steps of the same amplitude as the distance between said rows of characters and in a direction parallel to said columns of characters; signal responsive means having means for receiving data from an external source, and operable for controlling said position register means and said character matrix advance means for causing a succession of printed pages to be exposed onto said light sensitive medium.
 2. The non-impact page printer of claim 1 wherein: said first deflection system and first deflecting means consist of a first deflection yoke having first deflection coils and further including a dual digital to analog converter means coupled to dual current amplifier means for controlling the currents through said first deflection coils.
 3. The invention set forth in claim 2 additionally including a transient detector comprising: two dual differential comparator means connected to said first and second digital to analog converter and to said first and second current amplifiers; inverter means for selecting the output of said comparators according to the magnitude of said data received from said signal responsive means; AND gate means for assembling the output from said differential comparators with a control signal from said signal responsive means; means for controlling the timing of said scan and intensity control circuits by the output from said AND gate.
 4. The invention set forth in claim 1 additionally including a device for correcting the alignment of the display patterns on said cathode ray tube comprising: a. means for manually adjusting centering and deflection gain in two mutually perpendiculaR directions on said cathode ray tube; b. optical means for sensing the location of light patterns on said cathode ray tube; c. means for indicating that light is sensed by said optical means.
 5. The invention set forth in claim 4 wherein said means for advancing said character matrix comprises a stepper motor, and said stepper motor requires at least three pulses to advance said character matrix the equivalent of the distance between said rows of characters, and where said signal responsive means is equipped to select one; two or three of said pulses for advancing said character matrix, and where said signal responsive means controls said digital to analog converter to locate said rectangular light patterns on said cathode ray tube according to whether one, two or three pulses were selected.
 6. The invention set forth in claim 4 wherein said first deflection yoke and said second deflection yoke are replaced by a single deflection yoke, including coils for deflecting said electron beam in two mutually perpendicular directions and wherein said dual current amplifier is a summing amplifier receiving inputs from said digital to analog converters and from said scan current generators.
 7. The non-impact page printer of claim 1 wherein: said second deflection system and second deflecting means consist of second deflection yoke and second deflection coils. 